Are team buildings productive?

The #SizTheWorld team is excited for the Kaya 959 Easter Egg hunt this morning. It's a great team building exercise. What kind of team building activities have worked well for your organization in the past? Should the focus be on fun/relaxation (e.g. outings, games) or skills-focused (e.g., workshops, problem-solving tasks)? Do you feel the company is in a better position after the team buildings?